Field of the Invention. The present invention relates to oilfield tubulars and to threaded connection between two oilfield tubulars. More particularly, the invention relates to a threaded oilfield tubular connection with two shoulders.
Background of the Invention. Oilfield tubular members, such as drill-pipe, frequently have a larger ID in the tube section than the ID in the connectors in order to decrease weight and increase flexibility. Accordingly, the tube section may be upset and tool joints with a smaller ID welded to the ends of the tube section. In other applications, it is desirable to form an entire joint from an integral bar for economic and material availability reasons, but since one end has to be a box end for receiving the pin end of another joint, the threaded connection is not able to have a xe2x80x9cdouble shoulderxe2x80x9d which provides increased torsional strength.
Oilfield tubular connections with double shoulders are known in the art. U.S. Pat. No. 1,326,643 discloses a double shoulder connection. U.S. Patent illustrates a version of a double shoulder connection. More recent designs for double shoulder connections are disclosed in U.S. Pat. Nos. 5,549,336 and 5,908,212.
The disadvantage of the prior art are overcome by the present invention and an improved oilfield tubular connection is hereinafter disclosed.
In a preferred embodiment, the oilfield connection includes a box on one end of a tubular and a pin on the other end of the tubular, with mated threads joining the tubulars.
It is a feature of the invention that a double shoulder connection may be used to retrofit previously manufactured drill string members to provide the double shouldered connection.
A further feature of the invention is that the double shoulder connection may be provided on both the box end and the pin end of the connection, with one sleeve provided in the box and another sleeve provided on the pin.
A further feature of the invention is that the tubular member may be manufactured with two different IDs at its ends: a smaller ID for the pin and a larger ID for the remaining entire length of the joint, including the box.
Another feature of the invention is that the sleeve may be made from either a similar or a dissimilar material as the corresponding pin or box.
Another feature of the invention is that the sleeve may be retained in the box with one of an interference fit, a tapered fit, a threaded connection, or a weldment. The ID of the sleeve preferably approximates the ID of the pin.
These and further features and advantages of the invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.